472 'Natural History in 'Foreign Coimtries, 



thrown out from volcanoes, or to have fallen from the firmanent ; opinions 

 which it requires little expense of argument to disprove. The prevailing 

 hypothesis is, that the rock blocks have been detached from mountains, 

 more or less distant from their present position ; some referring to the 

 mountains in a northerly, and others to the mountains in a southerly, 

 direction. M. Hausmann himself is of opinion that the rock blocks in ques- 

 tion have been rolled in a direction from north-east to south-west, and sup- 

 ports the theory by referring to Braunschweig, Hanover, the valley of the 

 Weser, &c., where are found the porphyry of Elfdal and other stones 

 which abound in Dalecarlia, as well as in the neighbouring mountain chains. 

 In Mecklenburg, also, and Pomerania, are found the debris of the rocks of 

 Gottland and Oeland ; and the dispersion of these blocks extends even 

 through Denmark and into the interior of Sweden, as has been more fully 

 explained by M. Brongniart in a paper of which we have elsewhere taken 

 notice. ^Bulletin des Sciences.) 



HOLLAND AND THE NETHERLANDS. 



LibellulcB distinguished from .'E'shnae. — Monsieur M. L Van der Hoeven, 

 professor of natural history at Ley den, has given the following distinctions 

 of Libel lulae and jE's/mcs : — 



1. In the anterior wings of Libellulae, and near their base, is a humeral 

 or discoidal cellula, presenting the figure of a reversed rectangular triangle, 

 terminating in a point in the base. In jE'shnce, on the contrary, instead 

 of this triangle, there is found a cellula of greater size, and horizontally 

 shaped, while there is no difference between their anterior and posterior 

 wings. 



2. JE'shncB which have their eyes widely separated (such as the M'slina 

 forcipata of Fabricius, M. unguiculata), and forming the second division of 

 this genus in the system of M. Vander Linden {M'shna bononi^nsis) in 4to, 

 1820, have a triangular cellula, like that of Libellulae, but shorter and 

 more broad. In other respects, their anterior and posterior wings resemble 

 those of other JF/shnce^ which never occurs among Libellulae. ' Agrions 

 may, perhaps, be distinguished by the feebleness of their brachial nervures, 

 and the narrowness of their wings. {Annales des Sciences Naturelles, 

 December.) 



SWEDEN. 



The cartilaginous envelope of the brain in the ikfyxnie glutinosa, which 

 forms the cranium, has for a base a thin cartilage of a brown tint, and of a 

 structure peculiar to this subdivision of chondropterygian fishes, the Cyclo- 

 stommata. This supporting cartilage nearly resembles in form the lyre of 

 Apollo, consisting of an arch, of which the two sides are symmetrical. 

 Behind, this arch is supported by the anterior part of the vertebral column 

 and by the labyrinth ; and, before, it enlarges and terminates by two recur- 

 rent branches in form of an S reversed. (^RetziuSy Act. Acad. Sauv. Stock- 

 holm.) 



DENMARK. 



Ftora JDdnica. — Professor Hornemann lately read to the Society of 

 Copenhagen, a report upon a recent number of the Flora Ddnica. It con- 

 tains 50 species otcotyledonous plants, of which 18 have been added to the 

 Danish Flora. There are two, the Pjrola groenlandica and Pedicularis la- 

 nata, both from Greenland, which the Professor considers as new species. 

 Among 38 acotyledonous plants, the Alcyonidium attenuatum, from Green- 

 land, is also unedited. It may likewise be considered, that there are 22 new 

 species of this family, which have been discovered by Professor Schumacher, 



